The 3rd Generation Partnership Project (3GPP) TS 36.211, v11.0.0 (2012-10) and its latest incarnation 3GPP TS 36.211, v11.4.0 (2013-10), both entitled Physical Channels and Modulation, describe the physical channels and the modulation schemes used to realise the Long Term Evolution-Advanced (LTE-A) air-interface.
The modulation schemes for the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Control Channel (EPDCCH) are specified section 6.8.3 of TS 36.211, together with section 7.1.2, as being Quadrature Phase Shift Keying (QPSK).
The reliability of the PDCCH or EPDCCH was an important consideration in the control channel design. If resource allocation information for a Physical Downlink Shared Channel (PDSCH) conveyed by the PDCCH or an EPDCCH is incorrectly received, the decoding of the corresponding PDSCH will likely fail, which, in turn, will have a detrimental impact on overall system performance. Therefore, transmission techniques such as channel coding, spatial and frequency diversity were considered in the PDCCH and EPDCCH design to improve reliability of such channels.
However, interference may occur when a User Equipment (UE) experiences, for example, co-channel interference originating from either inter-cell UE communications or co-scheduled intra-cell UE communications; both of which can limit performance.